Dermatome with ultrasonic cutting blade

ABSTRACT

A dermatome assembly is operable to harvest a skin graft and includes an ultrasonic dermatome and a power supply. The ultrasonic dermatome includes a body and an ultrasonic blade assembly mounted in the body. The blade assembly includes a frequency generator and a cutting horn powered by the frequency generator. The cutting horn is spaced apart from the body so that the body is restricted from damping vibrational movement of the cutting horn. The dermatome assembly is operable to precisely control the thickness of the cut skin graft and also restrict the cutting horn from overheating.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/356,338, filed Jan. 23, 2012, entitled DERMATOME WITH ULTRASONICCUTTING BLADE, which is a continuation of U.S. application Ser. No.12/323,224, filed Nov. 25, 2008, entitled DERMATOME WITH ULTRASONICCUTTING BLADE, which claims the benefit of U.S. Provisional ApplicationNo. 60/990,867, filed Nov. 28, 2007, entitled DERMATOME WITH ULTRASONICCUTTING BLADE, each of which is hereby incorporated in its entirety byreference herein.

BACKGROUND

1. Field

The present invention relates generally to devices for harvesting skingrafts. More specifically, embodiments of the present invention concernan ultrasonic dermatome.

2. Discussion of Prior Art

A dermatome is a medical instrument for cutting skin grafts and has beenin use since the early 1900s. Prior art dermatomes include a blade witha straight razor-like edge and a head that can be adjusted to vary thewidth and thickness of the skin graft. Conventional dermatomes areeither manually operated or electrically powered. Powered dermatomes aregenerally able to cut skin grafts more easily and more precisely thanmanual dermatomes. One electrically powered dermatome includes a bladethat is driven in a side-to-side oscillating motion along the length ofthe blade edge and is powered by an electric motor and a mechanicaldrive.

Prior art dermatomes have a number of undesirable limitations. Forexample, conventional dermatomes require significant physical effort andcoordination to operate and typically require more than one person toperform the procedure of cutting a skin graft. In particular,conventional dermatomes require the user to apply a precise amount ofpressure to the dermatome while precisely controlling the speed at whichthe dermatome is drawn along the skin Powered dermatomes are alsonotorious for generating an excessive amount of mechanical noise.Furthermore, the mechanical drive of prior art powered dermatomes areprone to undesirable wear and failure after only 20-30 hours ofcontinuous use.

SUMMARY

Embodiments of the present invention provide an ultrasonic dermatomethat does not suffer from the problems and limitations of the prior artdermatomes set forth above.

A first aspect of the present invention concerns an ultrasonic dermatomebroadly including a body, an ultrasonic frequency generator, a bladeelement, and a gauge bar. The body includes a handle. The ultrasonicfrequency generator is mounted to the handle. The blade element presentsproximal and distal ends. The blade element is drivingly attached to thefrequency generator adjacent the proximal end and presents a cuttingedge along the distal end, with the cutting edge being operable to cut askin graft. The gauge bar is supported by the body and positionedadjacent the cutting edge to engage the skin The gauge bar and cuttingedge are spaced apart to present a graft opening through which the skingraft is operable to pass when cut. The blade element is supported bythe body to define a distal cantilevered blade section that includes thecutting edge. The distal cantilevered blade section is spaced apart fromthe body to restrict the body from damping ultrasonic energy transmittedfrom the ultrasonic frequency generator to the cutting edge.

A second aspect of the present invention concerns an ultrasonicdermatome broadly include a body, an ultrasonic frequency generator, anda blade element. The body includes a handle. The ultrasonic frequencygenerator is mounted to the handle. The blade element presents proximaland distal ends. The blade element is drivingly attached to thefrequency generator adjacent the proximal end and presents a cuttingedge along the distal end, with the cutting edge being operable to cut askin graft. The body presents a coolant channel that is fluidlyconnectable to a coolant source and extends through the handle andterminates at a channel outlet. The outlet is positioned adjacent thecutting edge, with the coolant channel being operable to supply coolantthrough the outlet and on the cutting edge while the skin graft is beingcut.

A third aspect of the present invention concerns a method of harvestinga skin graft broadly including the step of cutting the skin graft withthe cutting edge of an ultrasonic dermatome. The cutting step includesthe steps of vibrating the cutting edge to cut the skin graft andsimultaneously discharging coolant on the cutting edge.

Other aspects and advantages of the present invention will be apparentfrom the following detailed description of the preferred embodiments andthe accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Preferred embodiments of the invention are described in detail belowwith reference to the attached drawing figures, wherein:

FIG. 1 is a perspective of a dermatome assembly constructed inaccordance with a preferred embodiment of the present invention, withthe dermatome assembly including an ultrasonic dermatome and a powersupply connected by umbilical lines, and showing a skin graft beingharvested from tissue;

FIG. 2 is a schematic view of power supply shown in FIG. 1, showingvarious components of the power supply, including a coolant supply;

FIG. 3 is an upper perspective of the ultrasonic dermatome shown in FIG.1, showing a body of the dermatome, including a handle, a head, and alsoshowing a gauge bar assembly of the dermatome, with the umbilical linesextending from a proximal end of the handle;

FIG. 4 is a lower perspective of the ultrasonic dermatome shown in FIGS.1 and 3, showing the body and gauge bar assembly of the ultrasonicdermatome cross-sectioned to show an ultrasonic blade of the ultrasonicdermatome, with the ultrasonic blade including a frequency generator, abooster, and a cutting horn drivingly interconnected, and with thecutting horn cantilevered from the booster;

FIG. 5 is a fragmentary cross-section of the ultrasonic dermatome shownin FIGS. 1, 3, and 4, showing the head, the gauge bar assembly, and thecutting horn cantilevered within the head, with the head including anupper plate spaced above the cutting horn, a guide foot spaced below thecutting horn, and a blade cover attached to a distal end of the guidefoot, and also showing a gauge bar of the gauge bar assembly in alowermost position;

FIG. 6 is an enlarged fragmentary cross-section of the ultrasonicdermatome shown in FIGS. 1 and 3-5, showing vibrational movement of thecutting horn along a fore-and-aft vibrational axis, and showing thegauge bar in an uppermost position;

FIG. 7 is an exploded view of the ultrasonic dermatome shown in FIGS. 1and 3-6, showing sections of the handle attached to each other andshowing the handle removed from the head; and

FIG. 8 is an exploded view of the ultrasonic dermatome shown in FIGS. 1and 3-7, showing the handle section removed from one another and thebooster and frequency generator separator so that the frequencygenerator and proximal handle section cooperatively form a frequencygenerator module of the dermatome and the remaining components of thedermatome form a cutting module.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning initially to FIGS. 1 and 2, a dermatome assembly 20 is operableto remove a skin graft G from tissue T. The skin graft G removed by thedermatome assembly 20 is typically used in repairing an area of damagedskin, e.g., from burning, or for use in cosmetic surgery. The skin graftG may be harvested from tissue of a live patient or from a cadaver. Theillustrated dermatome assembly 20 is particularly effective underextended use, e.g., for use at a skin bank where skin grafts can beharvested throughout the day. The dermatome assembly broadly includes anultrasonic dermatome 22 and a power supply 24.

As will be discussed in greater detail, the power supply 24 drives theultrasonic dermatome 22 and provides a supply of coolant. The powersupply 24 broadly includes a frequency controller 26, a power amplifier28, a system controller 30, a power filter 32, power factor correction34, a power supply interface 36, a power output line 38, and a powersupply housing 40. The power supply 24 also receives power via an A/Cpower input line 42. In the usual manner, the power supply 24 provides apower signal to the dermatome 22 via the power output line 38 andthereby controls the vibrational frequency and amplitude. For example,the power supply 24 can be adjusted by the user to control thevibrational amplitude. This adjustment is particularly helpful toprovide efficient cutting operation as properties of the tissue T changeand as the thickness of the skin graft G changes. The power supply 24also is operable to automatically tune to the precise resonant frequencyof the dermatome 22. The power supply 24 also includes an overloadcircuit to detect when the dermatome 22 encounters too much resistance,e.g., due to the tissue T, and automatically shuts off power to thedermatome 22. In this manner, the power supply 24 protects itself fromdamage and restricts heat buildup in the dermatome 22, particularlyalong the cutting edge. Furthermore, the interface 36 includes a warninglight operably connected to the overload circuit and the warning lightprovides a visual indication to the user that the dermatome 22 isapproaching an overload condition. Thus, the user can shut down thedermatome 22 prior to reaching overload.

The power supply 24 also includes a coolant supply 44 operable to coolthe ultrasonic dermatome 22 during use, as will be discussed further.The coolant supply 44 preferably includes coolant container 46, a pump48, a pressure regulator 50, a thermal converter 52, a safety valve 54,and a controller 56. The pump 48 draws coolant from the container 46 andcirculates the coolant through the thermal converter 52, which acts as aheat exchanger and mixer to control coolant temperature. Some of thecoolant is discharged through the valve 54 and into a coolant line 58,and some coolant is returned to the container 46.

The dermatome assembly 20 includes connectors 60,62 and umbilical lines64,66 for interconnecting the dermatome 22 and the power supply 24. Inparticular, umbilical line 64 is connected to the power output line 38by connector 60 and transmits power from the power supply 24 to thedermatome 22. Umbilical line 66 is fluidly connected to the coolant line58 by connector 62 and transmits coolant from the coolant supply 44 tothe dermatome 22.

The illustrated coolant supply 44 preferably contains and supplies afluid coolant in the form of a conventional hepa-cleaner. However, theprinciples of the present invention are applicable where the coolantincludes another type of liquid or includes a gas, such as air or aninert gas. For instance, the coolant could comprise a moist stream ofair. While the illustrated coolant supply 44 is operable to cool theultrasonic dermatome 22 by providing a supply of fluid coolant, it isalso within the ambit of the present invention where the dermatomeassembly 20 includes another mechanism for cooling the dermatome 22,such as thermoelectric cooling. For certain aspects of the presentinvention, the dermatome assembly 20 may not include a coolingmechanism.

The components of the power supply 24 are all preferably contained inthe housing 40, but it is also within the ambit of the present inventionwhere the power supply components are alternatively housed. Forinstance, the coolant supply 44 could be housed separately from the restof the power supply 24. Also, at least some components of the powersupply 24 could be housed in the ultrasonic dermatome 22.

Turning to FIGS. 3-8, the ultrasonic dermatome 22 is powered by thepower supply 24 to harvest the skin graft G and broadly includes a body68, a gauge bar assembly 70, and an ultrasonic blade assembly 72. Aswill be discussed further, the blade assembly 72 is operable to vibrateat ultrasonic frequencies for cutting of the skin graft G.

The illustrated body 68 broadly includes a handle 74 and head 76 thatare removably attached to one another and cooperatively serve as achassis for the ultrasonic dermatome 22. The handle 74 comprises anelongated tubular structure and includes a pair of proximal and distalhandle sections 78,80 that are removably attached to one another andcooperatively present an internal chamber 82. In particular, the handlesections 78,80 include mating connector ends 84,86 that cooperativelyprovide a releasable fluid-transmitting joint for permitting access tothe chamber 82. It is within the ambit of the present invention wherethe releasable mechanism that holds the ends 84,86 together comprises aconventional connector that includes threaded connectors or fasteners.The handle sections 78,80 each present coolant channels 88 that arefluidly connected to each other at the joint and are sealed by gaskets90. As will be discussed, the handle sections 78,80 are separable topermit sterilization of the dermatome 22. However, it is also within thescope of the present invention where the releasably joint does nottransmit coolant.

Handle section 78 presents a proximal opening 92 that receives theumbilical lines 64,66. Handle section 80 also includes a distal flange94 operable to be attached the head 76, and the handle section 80presents a distal opening 96 that permits access to the chamber 82. Thehandle 74 also includes a contoured grip 98 attached to the handlesection 80 and a movable switch 100 slidably attached to the handlesection 78. The handle 74 is preferably manufactured from a metallicmaterial, such as stainless steel, but could include other materialssuitable for medical devices, such as plastics.

The head 76 presents proximal and distal head ends and includes sidewalls 102 that extend between the ends. The side walls 102 present upperand lower margins and are interconnected by an upper plate 104. Theupper plate 104 extends between the proximal and distal head ends. Theupper plate 104 includes a proximal section that is attached to the sidewalls along the upper margins and a distal section that extends towardthe lower margins of the side walls 102. As will be discussed, thedistal section serves to direct the skin graft G and presents aseparator surface 106 that extends in a proximal direction from a distalseparator edge 108. The upper plate 104 also includes an internalcoolant channel 110 that includes a supply portion 112, a lateralmanifold portion 114, and three angled portions 116 that fluidlycommunicate with the manifold portion 114 and extend to outlets adjacentthe distal separator edge 108. As will be discussed the coolant channel110 is operable to discharge coolant for cutting the skin graft G.

The head 62 also includes a removable lower guide foot 118 that presentsa transversely extending distal groove 120, and a removable blade cover122 received by the distal groove 120. The lower guide foot 118 isattached to the side walls 102 with fasteners 124, and is positioned sothat the distal groove 120 is positioned adjacent the distal separatoredge 108. The side walls 102, upper plate 104, and guide foot 118cooperatively present a head chamber 126 and a proximal opening 128 (seeFIG. 8) that permits access to the head chamber 126. The head chamber126 presents a thickness that tapers toward a distal end of the head 76,and a width that is substantially constant between the distal andproximal ends of the head 76. The head chamber 126 is operable toreceive the blade assembly 72, with the blade assembly 72 extending intoand out of the chamber 126 via the proximal opening 128.

The blade cover 122 is unitary and includes opposite ends and alaterally extending distal slot 130 that presents a slot width SW (seeFIG. 7). As will be discussed further, the distal slot 130 defines aneffective blade width of the dermatome 22. The head 62 is attached tothe handle 74 with threaded fasteners 131 that extend through holes inthe flange 94 and into the side walls 102. Furthermore, the head 62 andhandle 74 are attached so that channels 88 fluidly communicate withchannel 110, with the channels 88,110 being sealed by gaskets 90. Thus,the head 62 and handle 74 cooperatively form the body 68, with alongitudinal body axis A. The illustrated body 68 preferably has alength less than about 12 inches, but could be longer than 12 incheswithout departing from the scope of the present invention.

Turning to FIGS. 3-7, the gauge bar assembly 70 cooperates with theblade assembly 72 to determine the thickness of the skin graft G. Thegauge bar assembly 70 preferably includes a pair of bushings 132, aneccentric shaft 134, a gauge bar 136 pivotally mounted on the shaft 134,an adjustment knob 138, and a locking fastener 140 (see FIG. 7). Eachside wall 102 presents a lateral bore 142 positioned adjacent the distalhead end and adjacent the upper margin. The bores 142 are coaxial andeach are configured to receive a corresponding bushing 132 therein.

The eccentric shaft 134 presents opposite shaft ends 144 that define ashaft axis S, and a central cam 146 that interconnects the shaft ends144 and presents a cylindrical cam surface that is axially offset fromthe shaft axis S. The eccentric shaft 134 is rotatably mounted on thehead by inserting each shaft end 144 into a corresponding bushing 132.

The gauge bar 136 includes a rectangular gauge plate 148 that presentsupper and lower margins. The gauge bar 136 also includes a pair ofsleeves 150 fixed to the gauge plate 148 along the upper margin, withthe sleeves 150 presenting a common axis. The gauge bar 136 is rotatablymounted on the eccentric shaft 134 by extending the central cam 146through the sleeves 150. The gauge bar 136 also includes opposite endsslidably mounted in slots presented by the side walls 102. As the shaft134 is rotated about the shaft axis S, the sleeves follow the axis ofthe cylindrical cam surface. Thus, rotational movement of the shaft 134causes up-and-down movement of the gauge bar 136 within the slots of theside walls 102.

The adjustment knob 138 is attached to one of the shaft ends 144, withpivotal movement of the knob 138 causing the shaft 134 to rotate in thesame direction. The locking fastener 140 comprises a fastener that isthreaded into the knob 138 and can be adjusted into and out ofengagement with the corresponding side wall 102. Thus, the fastener 140is operable to selectively lock the adjustment knob 138 into a positionto restrict up-and-down movement of the gauge bar 136. While theillustrated gauge bar assembly 70 is preferable, it is also within thescope of the present invention where the gauge bar assembly 70 isalternatively constructed to engage the skin graft G and to cooperatewith the blade assembly 72 to control the thickness of the skin graft G.

Turning to FIGS. 4, 7, and 8, the ultrasonic blade assembly 72 isoperable to vibrate at a resonant frequency and broadly includes afrequency generator 152, a cutting horn 154, and a booster 156 thatinterconnects the frequency generator 152 and horn 154. The frequencygenerator 152 preferably comprises a piezoelectric transducer that isoperable to vibrate an output end 158 in an in-line direction along avibration axis V at a frequency of at least about 10 kHz. Morepreferably, the generator 152 vibrates at a frequency between about 20kHz and about 70 kHz during normal operation. Most preferably, thegenerator 152 vibrates at a frequency between about 30 kHz and about 40kHz. It is also within the ambit of the present invention where thegenerator 152 is another transducer that converts an electrical signalinto vibrational movement, such as a magnetostrictive transducer. Thegenerator 152 is operably coupled to the switch 100 so that thegenerator 152 can be turned on and off by the switch 100.

In the usual manner, the booster 156 is operable to tune the bladeassembly to a resonant frequency and includes a tuned booster section160 and a sleeve 162. The booster section 160 includes opposite proximaland distal ends 164,166 and a central portion that presents a maximumdiameter of the booster section 160, with the central portion taperingtoward each end 164,166. The sleeve 162 extends around the centralportion and supports the booster 156 within the handle 74. The booster156 is removably attached to the frequency generator 152. In particular,the proximal end 164 and the output end 158 include mating connectors.While the illustrated connectors comprise a bayonet-type connectorassembly, the principles of the present invention are applicable whereother types of connectors are used to mount the booster 156 to thefrequency generator 152.

Turning to FIGS. 4-8, the cutting horn 154 comprises a blade withproximal and distal ends and a blade axis B that extends between theends. The blade presents a distal cutting edge 168 perpendicular to theblade axis B, and the distal cutting edge 168 has a blade edge width W.The blade edge width W is preferably at least about one-half inch. Morepreferably, the cutting horn 154 can be provided with a blade edge widthW between about one inch and about six inches. The cutting horn 154presents a longitudinal cross section that tapers from the proximal endtoward the distal cutting edge 168 (see FIG. 5). In particular, theblade includes a proximal section that tapers from a first thickness T1to a second thickness T2, an intermediate section that tapers from thesecond thickness T2 to a third thickness T3, and a distal section thattapers from the third thickness T3 to the cutting edge 148. Preferably,thickness T2 is about one-third of thickness T1 and thickness T3 isabout one-half of thickness T2. However, the principles of the presentinvention are applicable where the cutting horn 154 presents alternativeshapes and dimensions. The blade also preferably includes three slottedopenings 170 that extend between the distal and intermediate sections(see FIG. 7). The illustrated openings 170 are elongated and eachpresent a longitudinal axis parallel to the blade axis B. Theillustrated openings 170 are also spaced side-by-side and are spacedapart from each other and from the cutting edge 168. In this manner, theopenings 170 direct vibrational energy along the blade axis B andrestrict vibrational energy from traveling in a lateral directionrelative to the blade axis B. It is within the scope of the presentinvention where the cutting horn 154 includes an alternative number orconfiguration of the openings 170. The illustrated cutting horn 154 ispreferably made of a titanium alloy, but could include other materials,such as stainless steel.

The cutting horn 154 is removably attached to the booster 156. Inparticular, the distal end 166 and the proximal end of the cutting horn154 include mating connectors. While the illustrated mating connectorscomprise a bayonet-type connector assembly, the principles of thepresent invention are applicable where other types of connectors areused to mount the booster 156 to the cutting horn 154.

The cutting horn 154 and booster 156 cooperatively provide a bladeassembly that preferably vibrates along the vibration axis V, and theblade axis B is preferably parallel to the vibration axis V. However, itis also within the scope of the present invention where the blade axisand vibration axis V are perpendicular to each other or present anoblique angle therebetween. The illustrated blade assembly preferablyvibrates at a resonant frequency of at least about 10 kHz. Morepreferably, the blade assembly has a resonant frequency between about 20kHz and about 70 kHz. Most preferably, the resonant frequency is betweenabout 30 kHz and about 40 kHz. The illustrated cutting edge 168 ispreferably perpendicular to the vibration axis V.

The frequency generator 152 is mounted within the proximal handlesection 78, with the output end 158 projecting distally. Furthermore,the booster 156 is mounted within the distal handle section 80 and issupported therein by the sleeve 162. However, the principles of thepresent invention are applicable where the booster 156 is spaced apartfrom and is unsupported by the handle 74. The cutting horn 154 is spacedwithin the chamber 82 and is entirely spaced apart from the gauge barassembly 70 and body 68. Thus, the cutting horn 154 is cantilevered frombooster 156.

The blade assembly 72 is positioned with the cutting edge 168 adjacentthe slot 130 of the blade cover 122. The blade cover 122 is arranged topermit the cutting edge 168 to cut the tissue T only along the width ofthe slot 130. The illustrated slot width SW is about the same as theblade edge width W, with the slot 130 and cutting edge 168 beingsubstantially coextensive with one another. However, it is also withinthe ambit of the present invention where the blade edge width W isgreater than the slot width SW and the blade cover 122 only permitscutting of tissue T along the slot width SW. In this manner, multipleblade covers having slots 130 of different widths can be used with thesame cutting horn 154 to provide different effective blade widths of thedermatome 22, with each cover thereby cooperating with the cutting horn154 to harvest skin grafts with a corresponding skin graft width. Inother words, the blade edge width W defines the maximum width of theskin graft G.

The illustrated dermatome 22 has a modular construction and isconfigured to be sterilized using conventional autoclave equipmentwithout damaging the frequency generator 152. Conventional frequencygenerators can be damaged by temperatures above 140° F., and autoclavesused to sterilize medical equipment traditionally exceed thistemperature limit. Consequently, the dermatome 22 is operable to bequickly separated for sterilization. In particular, the handle sections78,80 can be separated from one another, and the booster 156 can beseparated from the frequency generator 152 (see FIG. 8). Thus, thebooster 156 and frequency generator 152 comprise a frequency generatormodule of the dermatome 22 that can be sterilized at temperatures below140° F., e.g., by using ethylene oxide or ozone. The remainder of thedermatome 22 comprises a cutting module that can be sterilized using aconventional autoclave at temperatures above 140° F. The modulardermatome construction also permits quick replacement of the frequencygenerator 152 and cutting horn 154.

Turning again to FIGS. 4-8, the blade assembly 72 is operably mountedwithin the body 68 to define a dermatome cutting direction along theblade axis B and vibration axis V, with the cutting direction beingnormal to the cutting edge 168. The blade assembly 72 is mounted withinthe body 68 so that the cutting direction is preferably away from thehandle 74 and along the body axis A. However, it is also within theambit of the present invention where the cutting direction is toward thehandle 74 along the body axis A, or is in a direction not aligned withthe body axis A, e.g., perpendicular to the body axis A. Furthermore,the blade assembly 72 is mounted so that the body axis A and vibrationaxis V are parallel, but the axes A and V could be perpendicular orarranged in a non-parallel configuration without departing from thescope of the present invention.

The blade assembly 72 is also supported within the body 68 so thatvibration transmitted from the generator 152 to the cutting edge 168 isminimally damped. In particular, the cutting horn 154 is cantileveredfrom booster 156 so that the body 68 and gauge bar assembly 70 arerestricted from touching and thereby damping vibrational movement of thecutting horn 154. Furthermore, the booster 156 is supported by thehandle 74 at a location along the vibrational axis V where such supportwill cause minimal damping. It has been found that the blade assembly 72vibrating at a resonant frequency will have at least one dead area ornode along the vibrational axis V where the essentially no displacementalong the axis V occurs. This dead area provides a preferred locationfor laterally supporting the blade assembly 72. The illustrated booster156 preferably extends along the dead area for the blade assembly 72 andis supported along the dead area. Again, it is also within the ambit ofthe present invention for the booster 156 to be entirely spaced from thebody 68. Furthermore, the blade assembly 72 could be entirely devoid ofa booster 156 where the cutting horn is properly tuned to resonate atthe desired frequency. Vibrational energy transmitted from the generator152 causes the cutting edge 168 to move in an inline direction along theaxis V (see FIG. 6). During vibrational movement, the cutting edge 168preferably moves fore-and-aft through a total distance of less thanabout 0.010 inches.

Turning to FIGS. 4-6, the gauge bar 136 and cutting edge 168cooperatively define a graft opening that receives the skin graft G asthe skin graft G is cut and thereby determines the thickness of the skingraft. The illustrated gauge bar 136 is adjustable by movement of theknob 138 to shift up and down relative to the cutting edge 168 between alowermost position (see FIG. 5) and an uppermost position (see FIG. 6).Preferably, the illustrated gauge bar 136 is operable to be spacedrelative to the cutting edge 168 so that the graft opening presents anopening thickness O between about zero inches and about 0.040 inches.More preferably, the opening thickness O is operable to range from about0.002 inches to about 0.030 inches.

The cutting edge 168 is also positioned immediately adjacent the distalseparator edge 108, with the distal separator edge 108 being spacedabove the cutting edge 168. Preferably, the cutting edge 168 is spacedfrom the distal separator edge 108 a distance less than about 0.100inches. Thus, the distal separator edge 108 is operable to engage thecut skin graft G quickly after being cut from the tissue T and divertthe skin graft G onto the separator surface 106.

The separator surface 106 is spaced proximally from the gauge bar 136,with the separator surface 106 and gauge bar 136 cooperativelypresenting an open space 172 therebetween to receive the cut skin graftG as it moves past the cutting edge 168. Furthermore, the separatorsurface 106 is configured to carry the cut skin graft G away from thecutting horn 154. In particular, a distal portion of the separatorsurface 106 extends proximally from the distal separator edge 108 at aseparation angle α measured relative to the blade axis B. Preferably,the separation angle α is at least about 20 degrees. More preferably,the separation angle α is in the range from about 30 degrees to about 60degrees and, most preferably, is about 45 degrees. The illustratedseparator surface 106 also preferably presents a convex shape so thatthe skin graft G can feed smoothly through the open space 172 and out ofthe head 76.

The coolant channel 110 is configured to receive coolant from thechannels 88 and provide coolant directly to the cutting edge 168. Theangled portions 116 of the coolant channel 110 each extend to acorresponding outlet 174. The outlets 174 are positioned immediatelyadjacent and just proximal of the distal separator edge 108.Furthermore, the angled portions 116 preferably extend between theseparator surface 106 and the cutting horn 154, with the outlets 174just above the cutting horn 154. However, the principles of the presentinvention are equally applicable where the angled portions 116 andoutlets 174 are positioned below the cutting horn 154, e.g., byextending through the lower guide foot 118. It has been determined thatthe stream of coolant provided by the illustrated coolant channel 110 isoperable to sufficiently cool the cutting horn 154, particularly alongthe cutting edge 168, to restrict damage (e.g., cauterization) of thetissue T and the skin graft G. Furthermore, the coolant flow is operableto cool the space between the cutting edge 168, the tissue T, and theskin graft G. It has also been unexpectedly determined that this coolingconfiguration is operable to reduce the heat generated by ultrasoniccutting (e.g., by fluid cavitation and friction between the cutting horn154 and tissue T). Furthermore, this coolant flow can reduce frictionbetween the skin graft G and components of the dermatome 22. While theillustrated cooling device is preferable, for some aspects of thepresent invention, another cooling mechanism could be used, such as athermoelectric cooling.

The illustrated coolant channel 110 is also shaped and positioned tourge the skin graft G out of engagement with the cutting horn 154 andinto the open space 172. The illustrated angle portions 116 extendproximally from the outlets 174 to present a channel angle β relative tothe blade axis B. Preferably, the channel angle β is less than theseparation angle α. In this manner, the coolant flow out of the outlets174 is operable to direct the skin graft out of a direction along theblade axis B and into the open space 172. Furthermore, thisconfiguration permits coolant to flow into contact with the cutting edge168 while allowing the coolant channel 110 to extend through the upperplate 104. However, the principles of the present invention are equallyapplicable where the channel angle β is greater than the separationangle a. For example, the angled portions 116 could extend through thelower guide foot 118 below the cutting horn 154 and be directedupwardly, perhaps even perpendicular to the blade axis B, toward thecutting edge 168 so that cutting fluid would flow in an upward directionand thereby direct the skin graft G upwardly into the open space.

In operation, the dermatome assembly 20 is turned on by moving theswitch 100 to power the dermatome 22, which causes the frequencygenerator 152 to vibrate the cutting horn 154. Furthermore, coolant issimultaneously pumped by the coolant supply 44 via the umbilical line 66into the channels 88,110 and through the outlets 174 onto the cuttingedge 168. As the dermatome 22 is moved in the cutting direction acrosstissue T, the cutting edge 168 cuts the skin graft G by vibrating in thefore-and-aft direction. Simultaneously, coolant is discharged throughthe outlets 174 onto the cutting edge 168. In particular, the coolant isdischarged along the cutting direction to contact the cutting edge 168and impinge on the skin graft G and thereby direct the skin graft Gupwardly away from the cutting horn 154 and into the open space 172.Thus, the cut skin graft G is separated from the cutting horn 154 by theseparator surface 106 engaging the skin graft G and by the coolant flowengaging the cut skin graft G to deflect the skin graft G onto theseparator surface 106. As the dermatome 22 continues over tissue T, thecut skin graft G becomes longer and the separator surface 106 guides theskin graft G through the open space 172 and out of the head 76. Afterthe skin graft G is cut, the dermatome 22 can be sterilized byseparating the frequency generator module from the cutting module. Aftersterilization, the dermatome 22 can be reassembled for further use.

The preferred forms of the invention described above are to be used asillustration only, and should not be utilized in a limiting sense ininterpreting the scope of the present invention. Obvious modificationsto the exemplary embodiments, as hereinabove set forth, could be readilymade by those skilled in the art without departing from the spirit ofthe present invention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

What is claimed is:
 1. An ultrasonic dermatome comprising: a body; anultrasonic frequency generator mounted to the body; a blade assemblydrivingly coupled to the frequency generator so as to be selectivelyresonated at a natural frequency, said blade assembly including a bladeelement presenting a cutting edge operable to cut A skin graft, saidblade assembly presenting at least one node spaced from the cuttingedge; and skin-engaging structure spaced adjacent the cutting edge toengage the skin without substantially damping ultrasonic energytransmitted from the ultrasonic frequency generator to the cutting edge,said body being in supporting contact with the blade assembly at the atleast one node, such that the cutting edge is spaced from the body. 2.The ultrasonic dermatome as claimed in claim 1, said cutting edgecomprising a substantially straight uninterrupted edge that defines acutting direction normal to the edge.
 3. The ultrasonic dermatome asclaimed in claim 2, said blade assembly presenting proximal and distalends, said blade element presenting a longitudinal vibration axisextending between the proximal and distal ends, said cutting edgeextending in a lateral direction relative to the vibration axis.
 4. Theultrasonic dermatome as claimed in claim 3, said cutting edge beingpositioned transversely relative to the longitudinal vibration axis,with the cutting direction being along the longitudinal vibration axis.5. The ultrasonic dermatome as claimed in claim 2, said cutting edgepresenting an edge width dimension measured transversely to the cuttingdirection and operable to define the maximum width of the skin graft,said edge width dimension being at least about one-half inch.
 6. Theultrasonic dermatome as claimed in claim 5, said edge width dimensionbeing between about one inch and about six inches.
 7. The ultrasonicdermatome as claimed in claim 5, said skin-engaging structure includinga blade cover that partly covers the cutting edge and presents a coveropening defining an effective blade width dimension about the same asthe edge width dimension.
 8. The ultrasonic dermatome as claimed inclaim 1, said blade assembly including a proximal booster sectionadjacent a proximal end of the blade element and drivinglyinterconnecting the blade element and frequency generator, said boostersection being operable to tune the resonant frequency.
 9. The ultrasonicdermatome as claimed in claim 8, said blade section presenting a bladethickness that tapers in a distal direction.
 10. The ultrasonicdermatome as claimed in claim 9, said blade section presenting aplurality of tapered segments that define the blade thickness and eachtaper in the distal direction.
 11. The ultrasonic dermatome as claimedin claim 9, said blade section including a longitudinal slotted openingspaced proximally from the cutting edge and operable to restrictultrasonic energy from traveling laterally.
 12. The ultrasonic dermatomeas claimed in claim 8, said blade element and booster sectioncooperatively having a resonant frequency between about 30 kHz and about40 kHz.
 13. The ultrasonic dermatome as claimed in claim 1, said bodyincluding a head and an attached handle, with the head operablyreceiving the blade element therein, said skin-engaging structureincluding a gauge bar positioned adjacent the cutting edge to engage theskin, said gauge bar and cutting edge being spaced apart to present agraft opening through which the skin graft is operable to pass when cut,said head supporting the gauge bar.
 14. The ultrasonic dermatome asclaimed in claim 13, said gauge bar being shiftably mounted on the headto permit selective adjustment of an opening thickness dimension of thegraft opening.
 15. The ultrasonic dermatome as claimed in claim 14, saidopening thickness dimension being between about zero inches and about0.040 inches.
 16. The ultrasonic dermatome as claimed in claim 1, saidbody including a head and an attached handle, with the head operablyreceiving the blade element therein, said head defining at least in partthe skin-engaging structure, said head including a graft separatorsection that presents an angled separator surface that tapers in acutting direction to a distal separator edge extending along the cuttingedge and positioned immediately adjacent thereto, with the separatorsection operable to direct the cut skin graft out of engagement with thecutting edge.
 17. The ultrasonic dermatome as claimed in claim 16, saidskin-engaging structure further including a gauge bar positionedadjacent the cutting edge to engage the skin, said gauge bar and cuttingedge being spaced apart to present a graft opening through which theskin graft is operable to pass when cut, said head supporting the gaugebar, said separator section spaced between the blade element and gaugebar and operable to direct the cut skin graft into a space between theseparator section and gauge bar.
 18. The ultrasonic dermatome as claimedin claim 16, said blade section presenting a blade section axisextending transversely to the cutting edge, said angled separatorsurface extending proximally from the distal separator edge at anoblique angle relative to the blade section axis of about 45 degrees.19. The ultrasonic dermatome as claimed in claim 16, said distalseparator edge being spaced from the cutting edge a distance of lessthan about 0.100 inches.
 20. The ultrasonic dermatome as claimed inclaim 1, said body including a head and an attached handle, with thehead operably receiving the blade element therein, said handle includinga pair of hollow handle sections, with one section spaced between theother section and the head, said other section receiving the ultrasonicfrequency generator therein, said handle sections being removablyattached to one another so that the one section and head can be removedfrom the other section and ultrasonic frequency generator forsterilization.
 21. The ultrasonic dermatome as claimed in claim 1, saidat least one node comprising a single node.
 22. The ultrasonic dermatomeas claimed in claim 1, said at least one node being located proximallyrelative to the cutting edge.